How to render fire in cycles?
I tried making a smoke scene to see if I could answer this, and I had the same problem, I fixed it by baking the smoke simulation.  (go to the physics tab of the domain cube and under cache press bake.  

I hope that fixes the problem.

As a side note, for an easier smoke and fire material, you can use the Principled Volume BSDF.  This can be used for smoke and fire.

Here's a picture of the node set up and the result.  

The two settings you can change to change the look of the smoke is color and density.  I hope this is helpful to you. :)